Designing and engineering transistors for production using semiconductor processes typically involves trading off one or more performance parameters for one or more other performance parameters. Such performance parameters may include drain to source on resistance (Rdson), off breakdown voltage (BVoff) and on breakdown voltage (BVon), as some examples. For instance, in a laterally diffused metal-oxide-semiconductor (LDMOS) transistor, a dopant dose in a drift region (drift dose or DD) may be changed to modify the Rdson of a given LDMOS transistor. For example, increasing the drift dose of a semiconductor process used to produce a given LDMOS transistor will reduce the Rdson for that transistor as compared to an LDMOS transistor with the same physical configuration that is produced using a lower drift dose.
However, increasing the drift dose for a given LDMOS transistor may also reduce the BVon and/or the BVoff of the transistor, which may be undesirable. For example, increasing the drift dose used for a given transistor may cause an increase in electric field crowding (e.g., at a top surface of a silicon substrate) at a boundary between a gate dielectric of the transistor and field oxide formed using local-oxidation of silicon (LOCOS) disposed in the semiconductor substrate in a drift region of the transistor. This increase in electrical field crowding may reduce the breakdown voltages of the given transistor (BVon and BVoff), causing breakdown of the give transistor to occur at (or near) the gate dielectric and field oxide boundary at lower voltages than in the given transistor when a lower drift dose is used. Accordingly, improvements in Rdson are traded off for lower BVon and BVoff. As performance requirements for semiconductor devices increase, producing transistors that have acceptable Rdson values and acceptable breakdown voltage values may not be achievable using current approaches.